Manufacture of bimetallic articles



Patented Feb. 17, 1948 PATENT FFICE MANUFACTUBE 0F BIMETALLIC ARTICLES Marshall G. Whiteld, Garden City, N. Y., as-

signor, by menne ents. to Fairchild Engine and Airplane Corporation, New York, N. Y., a corporation of Maryland Application June 21, 1944, Serial No. 541,332

'l Claims. (Cl. 22-204) This invention relates to the manufacture lof bimetallic articles, such as bearings, bushings. and the like, and has particular reference to methods and apparatus for making the same of ferrous metal shells lined with aluminum containing metals including aluminum and aluminum base alloy.

Among the diiiiculties which has attended the manufacture of aluminum-lined bearings of sufficient strength to withstand heavy loads under rigorous operating conditions are the impaired internal alloy structure, or the bond between the bearing shell and the aluminum alloy, or both, which defects are largely due to unequal shrinking of the aluminum alloy in freezing after it hasbeen cast. Resulting bearings have either failed by stripping of the aluminum alloy liner wholly or partially from the backing shell or by radial or annular cracking within the liner.

In accordance with the present invention, methods are provided for lining ferrous metal backing shells with aluminum bearing alloy under such conditions that the freezing of the aluminum alloy does not impair its bond with the ferrous metal, and cracking, checking, splitting, or unequal strains within the liner which might lead to failure are precluded. Apparatus for conducting the methods to achieve the described results are also provided in accordance with this invention.

' The preferred method of this invention essentially comprises heating the surface of the steel or other ferrous metal bearing shell to be lined to a temperature at which it alloys with the molten .aluminum-containing bearing metal and, *while molten bearing metal lies in contact with the shell, rapidly freezing the same to the desired thickness required for the liner plus the amount which is to be removed by machining.

"This method is preferably carried out by im- `mersing 4the ferrous metal shellin a molten bath of the aluminum-containing bearing metal for a suillcient time to effect alloying therewith, and

` then, while still immersed in the bath, rapidly freezing that part of the aluminum bath overlying the shell by contacting it with a cold metal mass which abstracts heat from the layer of aluminum-containing metalon the ferrous metal shell. The bearing thus formed lsimmedlately vthereafter removed from the bath of molten metal` before the cold metal mass is heated to the temperature at which it ceases to keep the aluminum layer cooled and frozen.

" A modification involves differentially cooling whereby the rate of aluminum alloy freezing may be controlled. Such differential cooling is ef fected by composite cold metal freezing masses. portions of which have high heat capacity and others have lower heat capacity or conductivity. Alternatively, the cold metal mass may be coated with a partial insulator, or have applied to it in whole or in part a layer of lower or higher heat conductivity material, which in some applications may be adjustable relatively to the cold metal mass to obtain progressive freezing along selected areas of the aluminum-containing liner.

It will be seen that the methods and apparatus of this invention produce very sound bearings with resultant uniform dispersion of the alloying components of the liner, due to the extremely rapid freezing action induced by the cold metal freezing mass, which is an essential requirement of alloys containing tin and lead whose uniform dispersion is difllcult to obtain. Also, the novel methods of freezing the liner, whether conducted 80 vention, reference may be had tothe accompanying drawings, in which:

Figure 1 illustrates one method of making steel-backed aluminum alloy bearings or bushings according to this invention;

Fig. 2 illustrates a method of making dual bearings and also differential cooling of selected portions of the bearing liner during manufacture: and v Figs. 3 and 4 illustrate modified methods of differentially cooling the bearing liner.

Referring to the drawings, numeral Il designates a crucible or vat containing the bath Il of molten aluminum alloy with which it is desired to line the interior surface of the ferrous metal tubular bearing shell l2. The aluminum alloy bath il contains predominantly aluminum alloyed with a relatively small percentage or percentages of tin, nickel. silver. lead, or the like. As an example, an excellent aluminum alloy for bearing purposes is one comprising 94% commercially pure aluminum and 6% tin, although any desirable aluminum-containing bearing metal may be employed with equal facility. Although the invention is particularly adapted to ferrous selected areas of the aluminum-containing liner. metal shells lined with aluminum alloys. it may aesaeei be used with equal facility with other bearing metals, depending upon requirements.

The ferrous metal bearing shell I'2 is preferably a steel such as low carbon steel, or any alloy of steel commonly used or desirable for bearing shells. If only the inner surface of the shell I2 is to be lined or coated. the outer surface is preferably coated with a suitable stop-oil' solution, such as a lime or graphite solution, in order to prevent adhesion of the liner material thereto. The inner surface of shell I2, which is to be lined, is cleaned of foreign matter, but need not be chemically clean,

The shell I2 may be supported on a suitable rack I3 having spacers Il for holding the shell I2 in fixed position with its axis extending vertically. concentric with spaces I4 is an aperture in the rack I 3 for the reception of the reduced end of a relatively large core I5 made of material having a large heat capacity such as, for example, steel of low carbon content. Preferably, but not necessarily, core i! is formed of a steel alloy having approximately the same coefficient of thermal expansion as the aluminum alloy cornprising bath II. As an example, a nickel-steel alloy containing approximately one-third nickel, has about the same coeillcient of thermal ex pansion as aluminum, and provides the advantage that the liner and core contract. The core I5 may be pushed out of the bearing without the exercise of any considerable amount of force, when both core and bearing are cool.

The function of the core I5 is three-fold; it is of a dimension to provide an annular space between its outer surface and the inner surface of the shell I2 of the thickness desired for the liner, plus an adequate amount for machining; also it has a high heat capacity, causing rapid heat abstraction from the aluminum alloy in the annular space between the outer surface of the core I5 and the inner surface of shell I2, and it expands on abstracting heat from the hner to apply pressure thereto whlle the liner cools down to approximately room temperature. By a cold core I5 is meant cold in the sense that its temperature before immersion in the molten bath I I is materially lower than the temperature of the bath, say approximately room temperature. Means may be provided for cooling core I5, such as by circulating a liquid therethrough or by llling it with a material having higher heat capacity than the solid steel through the required temperature range.

In conducting the process of this invention, the steel shell I2, supported on rack I3, is immersed within the molten bath II, and retained therein for a sufficient time for at least the inner surface ofthe shell I2 to achieve the temperature of the molten bath II, at which time the aluminum of the bath alloys with the ferrous metal on the inner surface of the shell I2 to form a ferro-aluminum alloy at the interface. 0rdinarily, due to its thinness, the heat capacity of the steel shell I2 is relatively low, and hence the time required for heating the shell to the alloying temperature and the alloying action between the aluminum and the steel may require less than a minute. By means of the interface alloy, the aluminum alloy becomes bonded to the shell I2.

Immediately upon formation of the interface alloy. the cold core II is inserted within the shell I2, being centered with respect to the shell by reason of the cooperation of the reduced extension I6 thereon with a centering hole in the rack I3. The core I! being cold, immediately drawer heat from the surrounding aluminum alloy, and. inasmuch as the most of the surrounding aluminum alloy lies in the annular space between the inner surface of shell I2 and the exterior' surface of core I5, that aluminum alloy freezes rapidly. Such freezing takes place in a matter of seconds, although the time may be more, depending upon the volume of the annular space. Thereupon the rack I3 bearing the shell I2, core I5, and the frozen aluminum alloy liner Il be. tween the shell I2 and the core I5 is withdrawn from the bath II and cooled in air. Such removal must be effected before the core Ii is heated to a temperature such as to cease abstracting heat from the intervening aluminum alloy liner I1, so that the latter remains frozen to the shell I2. The aluminum alloy liner does not bond to the core I5 because the surface of the latter has not been heated to the temperature at which the alloying necessary to aluminum bonding can take place, and it may be graphitecoated as an additional precaution.

During air cooling of the liner after removal from the molten bath II, the core I5 gives support and applies radial pressure to the liner I1, because the shell I2 is cooled rapidly in air and thus contracts somewhat while the core I5 con tinues to abstract heat from the liner I1 and hus expands. This expansion of core I5 results in the application of uniform radial pressure between the aluminum liner I1 and the interior surface of the shell I2 and this pressure precludes impairment of the bond between them. which otherwise would tend to rupture owing to unequal contraction of the liner I1 and the shell I2. This uniform radial pressure while cooling also effects uniformity of liner structure throughout, without internal strains.

Upon cooling to near room temperature the bearing comprising shell I2 and its liner I 1 may be readily stripped from the steel core I5, this stripping being facilitated if the core I5 is made of a material having about the coeilicient of expansion of aluminum, such as the nickel alloy mentioned.

The aluminum alloy liner I'I is accordingly bonded to the steel shell I2 through the intervening ferro-aluminum alloy between the shell I2 and the liner I'Ifand is homogeneous and free ofinternal strains, cracks or checks, with the result that a very sound bearing adequate to withstand heavy loads for all machine purposes is provided. It is believed that the rapid freezing and radial pressure effected by the cold core I5 causes the favorable formation of the lining I1 with uniform dispersion of any alloying metal contained in the aluminum.

The bearing shell thus formed may be completed in the usual way by machining the inner surface of the liner I1 to the proper dimensions. and providing it with oil holes and grooves, as desired.

Dual bearings or bushings having bearing metal layers bonded to both inner and outer surfaces of the shell may be formed as illustrated in Fig. 2. After the ferrous metal shell I5 has been heated to the proper alloying temperature in the molten metal bath I I, the cold core I5' is inserted in the manner andfor the purpose described and simultaneously a cold sleeve of the similar properties of high heat capacity as core I5' may be placed around shell I2, as shown in Fig. 2. The sleeve I8 is centered with respect to shell lI2 as on rack I3, to provide an annular space II of the proper thickness. The molten bearingY metal in this annular space. I9 freezes quickly by reason of abstraction of heat therefrom by the' cold sleeve IB in the same manner as described in connection with the cold core I5.

After removal from the molten metal, sleeve I8, like core I5 or I5', continues to abstract heat from the adjacent bearing metal layer I9.

Where only external bearings or bushings are to be made, sleeve I8 will be used alone without core I5 and the inner surface of shell I2 will be coated with a suitable stop-olf solution in the manner described. y

Fig. 2 also illustrates an arrangement whereby the rate of freezing of the aluminumalloy liner within a bearing may be maintained substantially uniform throughout its axial length bydfferentially cooling the same. This'method has advantage in the case of long bearing shells, or multiple shells which are to be severed into shorter lengths, since the cooling rate at the axial center of the shell is different than that at the ends of the shell. By making the cold core I5' composite, with the outer ends of material having lower thermal conductivity than the center section 2 I, the heat is abstracted from the liner at the center section at about the same rate that the heat is abstracted therefrom at its end sections. Thus, the core I5' may be made of a steel center section 2| and cast iron end sections 20, cast iron having a lower conductivity than steel. The use of a composite shell I5' of the construction described precludes maintenance of molten or plastice center portions of the liner I1 after the ends thereof have frozen or solidified. In the same way, sleeve I8 may be made composite.

'I'he modification of Fig. 3 attains the same or similar end as that procured by the dierential cooling arrangement of Fig. 2, except that the core I5" is provided with partially heat-insulated ends 22 which may be ceramic or other insulating layers, so as to not conduct heat away from the aluminum alloy liner I1" as rapidly as does the center section 23 from the core I5".

Progressive freezing of the liner I'I'" may be obtained by providing an insulating sleeve 2l which is axially adjustable along the steel core 15'". Thus as the aluminum liner Il'" begins to freeze, the sleeve 2l is gradually withdrawn, as indicated by the dotted lines in Fig. 4, to progressively cool the sleeve from the lower end to the upper end at a uniform or non-uniform rate, as the case may be, depending upon the rate of withdrawal of sleeve 24 and whether or not the withdrawal is continuous or step-by-step. In this way the structure of the aluminum alloy liner may be controlled from one end of the bearing to the other. In any case, the exterior of the steel shell I2 may be'heat-insulated after withdrawal from bath Il to retard cooling, or it may be quenched or otherwise cooled to hasten freezing of the liner radially inwardly.

It will be observed that in each instance the cold core, I5, I5", or I5", as well as cold sleeve Il, extends beyond the ends of the shell I2 and the heat capacity of these extended portions also contributes to the freezing of the aluminum alloy liner by abstracting heat therefrom. Accordingly. these extensions cool the liner directly at its outer ends, and indirectly at its axial center zone by conduction of heat abstracted therefrom through the body of the core toward the extended opposite ends thereof. This advantage combined with the dierential heat abstraction anorded by the composite or partially insulated cores of Figs.

6 2 to '4. inclusive, enables accurate controlof the cooling ofthe linerin accordance with requirements.

It will be understood that different aluminum alloys require different cooling rates in order to obtain the unstrained structure desired for the liner, and this also applies to bearing metal liners made of alloys containing smaller percentages of aluminum, or alloys'not containing aluminum, such as alloys of various desirable compositions whose cooling rates may be controlled to advantage in accordance with the present invention.

It will also be understood that the invention is equally applicable to bushings and other articles of any shape, including straight or curved strips, involving the controlled freezing of a bearing metal liner or layer to one or both surfaces of a backing member of steel or other material to which the dissimilar metal is bonded or otherwise secured, that the term bearing as used herein and in the claims includes such bushings, straight or curved strips and the like, and that the term liner" as used herein and in the claims means the layer of aluminum-containing metal that is applied to the metal base or shell of any shape or dimensions.

v Althoughcertain embodiments of the method and apparatus of this invention have been illustrated and described herein, the invention is not limited thereby but is susceptible of changes in detail and form within the scope of the appended claims.

I claim:

l. The method of lining a bearing shell with lining metal, which consists in preliminarily conditioning the surface of the shell by immersing the same in a bath of the lining metal in the molten state, freezing a layer of said molten lining metal on said surface by transferring heat therefrom to a cold body in contact therewith, and applying pressure to said freezing lining metal as it cools by means of the thermal expension of the body as it is heated by said transfer of heat thereto from the lining metal without removing the same from said bath.

2. The method of lining the inner surface of a tubular metal bearing shell with lining metal, which consists in preliminarily conditioning said surface by immersing the same in a bath of the lining metal in the molten state, and introducing a, cylindrical cold metal body into the center of said shell ;while immersed in the bath to thereby freeze an annular layer of the'lining metal to the said surface of the shell by transferring heat from said layer to said body, and then removing said shell, liner, and body from said bath for cooling the whole.

3. 'I'he method of lining the surface of a tubular metal bearing shell with lining metal, which consists in preliminarily conditioning said surface by immersing the same in a bath of the lin ing metal in the molten state, and -placing a tubular cold metal body about said shell while immersed in the bath tothereby freeze an annular layer of the lining metal to the said surface of the shell by transferring heat from said layer to said body, and then removing said shell, liner. and body. from said bath for cooling the whole.

4. The method o f lining the inner and outer surfaces of a tubular metal bearing shell with lining metal, which consists in preliminarly conditioning said surfaces by immersing the same in a bath of the lining metal in the molten state, passing a tubular cold metal body about said shell and introducing a cylindrical cold metal 7 body into the center of said shell while immersed in the bath to thereby freeze anannular layer of the lining metal to the said surfaces of the shell by transferring heat from said layers to said bodies, and then removing said shell. liner. and bodies from said bath for cooling the whole.

5. The method of applying a layer of aluminum-containing metal to the surface of a ferrous metal article, which consists in immersing the article in a bath of the molten aluminum-containing metal for a sumcient time to form a ferroaluminum alloy at the interface between the surface of thc article and the molten aluminumcontaining metal in contact therewith, forming between said alloyed surface of said article and a cold metal mold spaced therefrom a layer of the aluminum-containing metal of the desired thickness, and freezing the said layer on said surface of the article by transferring heat from said layer to said cold metal mold without removing the same from said bath, whereby said layer is permanently bonded to said ferrous metal article when cooled.

6. The method of applying 9, layer of aluminum-containing metal to the surface of a ferrous metal article, which consists in immersing the article in a bath of the molten aluminum-containing metal for a sufficient time to form a ferroaluminum alloy film on the surface of the article at the interface between that surface and the molten aluminum-containing metal ink contact therewith, forming between said alloyed surface film of said article and a mold spaced therefrom a layer of the aluminum-containing bath metal of the desired thickness without removing the same from the bath, initially freezing the said layer on said surface of the article without removing the same from said bath, removing the article and said layer from the bath. and cooling the same substantially to room temperature.

whereby said layer is permanently bonded to said ferrous metal article through said ferro-alumni num film.

7. The method of applying a layer of alumi' num-containing metal to the surface of a ferrous metal article, which consists in immersing the article in a bath of the molten aluminum-containing metal for a sufficient, time to form a ferroaluminum alloy film on the surface of the article at the interface between that surface and the molten aluminum-containing metal in contact therewith, forming between said alloyed surface film of said article and a mold spaced therefrom a layer of the aluminum-containing bath metal of the desired thickness without removing the same from the bath, simultaneously removing the article and mold and the intervening layer of .aluminum-containing metal as a. unit from the bath, and then cooling the same substantially to room temperature, whereby said layer is permanently bonded to said ferrous metal article through said ferro-aluminum alloy film.

MARSHALL G. WHITFIELD.

REFERENCES CITED The following references are of record in the nle of this patent:

UNITED STATES PATENTS Number Name Date 2,156,998 McCullough May 2, 1939 1,343,128 Halverson June 8, 1920 1,332,975 Donaldsn Mar. 9, 1920 1,652,445 Lee Dec. 13, 1927 2,157,453 Jaeger May 9, 1939 851,684` Monnot Apr. 30, 1907 853,716 Monnot May 14, 1907 1,789,979 Jones et al Jan. 27, 1931 2,265,243 McCullough et al. Dec. 9. 1941 960,328 Howard June 7, 1910 

